Time is a critical component of computer enabled DRM (Digital Rights Management) systems, especially when they are implemented on top of untrusted environments (such as computer operating systems such as Microsoft Windows, Linux, Macintosh Operating System, or hardware in consumer electronic devices). Since users can fully interact with and access those systems, they are able to fake, replace, tamper, or remove some of the timing related operations performed or used by the DRM system.
Timing operations are managed by the operating system itself. User space processes (software) ask the operating system kernel (ring zero) for a time request (performing the SYS_gettimeofday system call, for instance, in the Macintosh operating system Leopard). Therefore there are many ways to return faked or tampered time indications to user space processes. These actions can be performed without modifying the targeted process virtual memory spaces using for instance API hooking or kernel patches as well known in the field. This is one of the most critical threats to the integrity of content (audio and video) rental DRM systems since one needs to ensure that time has not been modified or its rate changed (in order to pass slower for instance).